Is there any harm in buying a knockoff speedlight? I don't have the $100+ for a genuine Nikon speedlight and I am noticing some cheap ($30) speedlight knock-offs for sale. What would I be loosing versus buying a genuine speedlight?

1. Would it not be as controllable (it is TTL)?
2. Would the light be off white (it lists it as 5600K, but I doubt that )?
3. Would it eat lots of battery life?
4. Would it not be as bright?

Also, I recently got an extension tube. When I use it with my 70-210, I have to zoom to focus. What is my effective focal length going to be like? The centre of the range? The widest point? How many mm in extension tube would I need to get 1:1?

I will answer part of your question & leave the rest to others. When the extension tube/bellows is equal to the focal length of the lens you will have a 1:1 macro. i.e. 35mm lens+35mm extension = 1:1.

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I have a 70-210 lens, what will I need to get 1:1? That's what I need to know. As you may or may not know with a zoom lens and an extension tube, zooming actually focuses.

I have also considered getting a reversing ring, as doing a little handheld shooting with the 50 held in fron reversed got some great results, albeit lots of vignetting (probably because of my handholding).

generally i believe knock offs dont have all the compatibility or/and functions.. or reliability while im at it

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Well, considering I will be using totally manual shooting anyways (this would only be studio/product sort of photography) and I use all manual anyways, that isn't much of a problem. And, when I can buy 5+ for the price of one good speedlight, reliability (while very nice) isn't a big issue either.

Also, does anyone know if any knockoffs are any good in particular? Like one good seller, or one good "brand" (maybe just a value brand?).

Well, considering I will be using totally manual shooting anyways (this would only be studio/product sort of photography) and I use all manual anyways, that isn't much of a problem..

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Forget it... power is not variable.

If your intention is a "strobist" setup with the flash on a stand bounced in an umbrella, you can find some 285s, 283, or old sunpaks on ebay that should serve you well. Just be careful of trigger voltages.

[EDIT]

Is that ebay ad for the flash correct... GN of only 24? That's not very powerful.

I will answer part of your question & leave the rest to others. When the extension tube/bellows is equal to the focal length of the lens you will have a 1:1 macro. i.e. 35mm lens+35mm extension = 1:1.

Click to expand...

I have a 70-210 lens, what will I need to get 1:1? That's what I need to know. As you may or may not know with a zoom lens and an extension tube, zooming actually focuses.
.

Click to expand...

i think Ron made it as straight forward as it needed to be... but youre extension tube will need to equal your focal length for a 1:1 ratio... it only makes sense. since you have 70-210 to work with and you wanted to shot at 80mm focal length ud need a 80mm extension to have a 1:1. Zoom focuses?